U.S. patent application number 10/761408 was filed with the patent office on 2004-12-16 for light emitting diodes and planar optical lasers using iv semiconductor nanocrystals.
Invention is credited to Hill, Steven E..
Application Number | 20040252738 10/761408 |
Document ID | / |
Family ID | 32777015 |
Filed Date | 2004-12-16 |
United States Patent
Application |
20040252738 |
Kind Code |
A1 |
Hill, Steven E. |
December 16, 2004 |
Light emitting diodes and planar optical lasers using IV
semiconductor nanocrystals
Abstract
Lasers and LEDs are provided which are implemented with rare
earth doped group IV semiconductor nanocrystal material.
Inventors: |
Hill, Steven E.; (Castile
Rock, CO) |
Correspondence
Address: |
DOWELL & DOWELL PC
2111 Eisenhower Ave.
Suite 406
Alexandria
VA
22314
US
|
Family ID: |
32777015 |
Appl. No.: |
10/761408 |
Filed: |
January 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60441413 |
Jan 22, 2003 |
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60441485 |
Jan 22, 2003 |
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60450661 |
Mar 3, 2003 |
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Current U.S.
Class: |
372/43.01 ;
257/E33.003 |
Current CPC
Class: |
H01S 3/2383 20130101;
H01S 3/2391 20130101; H01L 33/18 20130101; H01S 3/1628 20130101;
H01S 3/063 20130101; H01S 3/0637 20130101; H01L 33/343 20130101;
H01S 3/169 20130101; H01S 3/0602 20130101 |
Class at
Publication: |
372/043 |
International
Class: |
H01S 005/00 |
Claims
We claim:
1. An LED comprising REDGIVN (rare earth doped group IV
nanocrystal) material.
2. The LED of claim 1 comprising in sequence: a conductive
substrate and/or bottom cladding; the REDGIVN in a REDGIVN film; a
conductive and transparent layer on top of the REDGIVN film; a
first contact on top of the conductive and transparent layer and a
second contact on the substrate; wherein the LED is turned on by
applying a voltage across the first contact and the second
contact.
3. The LED of claim 2 wherein: the substrate is selected from a
group consisting of: comprises p or n silicon substrate or
Transparent metal oxide semiconductors such as Zinc Oxide and III V
compound semiconductor substrates, and diamond substrate; the
REDGIVN layer is a silicon rich silicon oxide (SRSO) film
containing silicon nanocrystals doped with a rare-earth precursor;
the conductive and transparent layer comprises a poly-silicon
layer.
4. An LED according to claim 3 further comprising a small aperture
is etched through the first contact to allow emitted light out.
5. An LED according to claim 3 wherein the first contact is a
serpent contact to allow emitted light out.
6. An LED according to claim 1 comprising additional rare earth
dopants in the REDGIVN layer so as to produce multiple colours.
7. An LED according to claim 6 comprising rare earth dopants for
red, green and blue so as to produce white light.
8. An LED according to claim 1 comprising a plurality of layers of
REDGIVN each separated by a buffer layer, and each containing a
respective rare earth dopant.
9. An LED according to claim 8 wherein said plurality of layers of
REDGIVN comprise three layers, one each for red, blue and green
light.
10. An LED according to claim 9 wherein the rare earth ion are
selected from a group consisting of: for blue light:
Tetrakis(2,2,6,6 tetramethyl-3,5-heptanedionato)cerium(IV) and
Ce(TMHD).sub.4; for a green light:
Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)erbium (III)
Er.sup.+3(THMD).sub.3; for a red light:
Tris(2,2,6,6-tetramethyl-3,5-hept- anedionato)europium (III) and
Eu(TMHD).sub.3.
11. An LED according to claim 1 wherein the conductive substrate
and/or bottom cladding are also transparent so as to allow some
light to exit out the bottom of the device.
12. An array of LEDs each in accordance with claim 1.
13. An array of LEDs according to claim 12 wherein different rare
earth dopants are used in respective subsets of the array.
14. An array of LEDs according to claim 12 arranged in groups of
three, each group of three including a red light LED, a green light
LED and a blue light LED so as to produce an overall white light
LED.
15. An array of LEDS according to claim 12 wherein each LED is
individually actuatable.
16. A group of three LEDS according to claim 1 wherein each of the
three LEDs has a respective different rare earth dopant so as to
produce one of red, green and blue light.
17. The group of LEDs according to claim 16 wherein each of the
three LEDs is individually actuatable.
18. The group of LEDs according to claim 16 wherein the group of
LEDs is collectively actuatable.
19. An optical laser comprising REDGIVN material.
20. An optical laser according to claim 19 comprising: at least one
waveguide comprising a REDGIVN channel; at least one feedback
element(s) defining a laser- laser-resonator cavity in the
waveguide so that laser light is output from the waveguide when
pumped; a pump source.
21. An optical laser according to claim 20 wherein the pump source
is a broadband optical pump source.
22. An optical laser according to claim 20 wherein the pump source
is an electrical pump source.
23. An optical laser according to claim 20 comprising a substrate
and/or bottom cladding below the waveguide and a top cladding.
24. An optical laser according to claim 20 wherein the laser cavity
has a size, which is tuned to an excitation wavelength of the rare
earth dopant.
25. An optical laser according to claim 20 wherein the at least one
feedback element(s) comprise a first highly reflective mirror, and
a second output coupler mirror which is partially reflective.
26. An optical laser according to claim 20 wherein the at least one
feedback element(s) comprise a first Bragg grating which is highly
reflective, and a second Bragg grating which is which is partially
reflective.
27. An optical laser according to claim 20 wherein the feedback
elements are frequency selective, and are tuned to be most
reflective near a resonant frequency of the cavity.
28. An optical laser according to claim 20 further comprising means
for varying the wavelength(s) reflected by the feedback element(s)
and varying the effective length of the resonator cavity to thereby
tune the laser to a selected wavelength.
29. An array of lasers according to claim 20 formed on a common
substrate.
30. The array of lasers according to claim 29 wherein each laser of
the array of lasers has resonant characteristics and dopants
selected to produce a respective different wavelength.
31. The array of lasers according to claim 30 wherein each laser
has a respective laser cavity having a different length.
32. A laser according to claim 20 further comprising a Diffraction
Bragg reflector (DBR) grating formed into or close to the waveguide
is used to tune the wavelength of light supported in the waveguide
cavity.
33. A laser according to claim 20 wherein the resonance
characteristics of the waveguide cavities are individually selected
by varying the pitch of the reflection gratings used to define the
cavities which, along with the effective refractive index for the
propagated optical mode, determines the wavelengths of light
reflected by the gratings.
34. A laser according to claim 20 comprising a surface-relief
grating forming a distributed Bragg reflection grating fabricated
on a surface of the wave guide.
35. A laser according to claim 20 comprising: a conductive
substrate having a first electrical contact; a transparent
conductive cladding buffer; a layer comprising the wave guide, a
second electrical contact on top of the REDGIVN channel; an
electrical pump source.
36. An optical laser according to claim 35 wherein the at least one
feedback element(s) comprise a high reflecting mirror and output
coupler at opposite each end of the waveguide to form the
resonating cavity.
37. A laser component comprising: a thin film containing REDGIVN
and having a plurality of waveguides defined by channels within the
substrate; one or more feedback elements for providing optical
feedback to the waveguides to form a respective laser-resonator
cavity in each wave guide with a distinct resonance characteristic
to provide lasing action at a selected wavelength when pumped,
wherein injection of pump light at one or more suitable wavelengths
into the laser-resonator cavity causes output of laser light at the
selected wavelength in accordance with a longitudinal cavity mode
of the cavity.
38. A laser according to claim 37 further comprising: a ferrule
having a plurality of spaced-apart attachment sites; and a
plurality of optic fibers attached to the ferrule at a respective
one of the plurality of spaced-apart attachment sites, each optical
fiber also being connected to receive light from a respective one
of the resonator cavities.
39. A laser according to claim 37 wherein the laser-resonator
cavities have a plurality of widths on a substrate surface to
thereby define a plurality of effective indices of refraction for
the cavities, the wavelength of a longitudinal cavity mode being
dependent thereon.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Nos. 60/441,413 filed Jan. 22, 2003, 60/441,485 filed
Jan. 22, 2003 and 60/450,661 filed Mar. 3, 2003.
FIELD OF THE INVENTION
[0002] The present invention relates to applications of group IV
semiconductor nanocrystals, more specifically, light emitting
diodes and planar optical lasers.
BACKGROUND OF THE INVENTION
[0003] The dominant semiconductor material is silicon and it has
been called the "engine" behind the information revolution. A
downside of silicon is that it has poor optical activity due to
it's indirect band gap which has all but excluded it from the
optoelectronics whose exponential growth rate surpasses even the
vaunted "Moore's Law" of silicon integrated circuits. In the past
two decades there have been highly motivated attempts at developing
a silicon-based light source that would allow one to have digital
information processing and optical communications capabilities in a
single integrated silicon-based integrated structure. For this to
be of any practical use, several important issues need to be
addressed than just generating light. The silicon Light Emitting
Diode (LED) source should (1) emit at a technologically important
wavelength, (2) achieve its functionality under practical
conditions (e.g. temperature and pump power), and (3) offer
competitive advantage over existing technologies.
[0004] One of the materials that has gathered much international
attention is erbium (Er) doped silicon (Si). The light emission
from Er-doped Si occurs at the technological important 1.5 micron
(.mu.m) wavelength. An Er doped Si emitter has the minimum optical
absorption of silica-based optical fibers. By exciting the first
excited state of the intra-4f shell atomic transition to the ground
state of the Er.sup.3+ (.sup.4I.sub.13/2-.sup.4I.sub.15/2) it emits
photons at the 1.5 micron wavelength. Furthermore it has been shown
that both theoretical and experimental results suggest that Er in
Si is Auger-excited via carriers, generated either electrically or
optically, that are trapped at the Er-related defect sites and then
recombine, and that this process can be very efficient due to the
strong carrier-Er interactions.
[0005] If one tries this strong carrier-Er interaction in Er-doped
bulk Si one sees a very reduced efficiency of the Er.sup.3+
luminescence at practical temperature and pump powers down to
impractical levels. In recent papers it has been demonstrated that
using silicon-rich silicone oxide (SRSO) which consists of Si
nanocrystals embedded in a SiO.sub.2 (glass) matrix reduces many of
the problems associated with bulk Si and can have efficient room
temperature Er.sup.3+ luminescence. The Si nanocrystals act as
classical sensitizer atoms that absorb incident photons and then
transfer the energy to the Er.sup.3+ ions, which then fluoresce at
the 1.5 micron wavelength with the following significant
differences. First, the absorption cross section of the Si
nanocrystals is larger than that of the Er.sup.3+ ions by more than
3 orders of magnitude. Second, as excitation occurs via Auger-type
interaction between carriers in the Si nanocrystals and Er.sup.3+
ions, incident photons need not be in resonant with one of the
narrow absorption bands of the Er.sup.3+. However, existing
approaches to developing such Si nanocrystals have only been
successful at producing up to 0.03 percent atomic weight and this
is not sufficient for practical applications, for example erbium
100 atomic percent of 5.81.times.10.sup.22 atoms cm.sup.-3, see
Applied Physics Letter Vol 72, Num 9, 2 Mar. 1998 pp1092-1094, J.
Sin, M. Kim, S. Seo, and C. Lee.
[0006] In the past history of the semiconductor development silicon
has been considered unsuitable for the optoelectronic applications.
This is from the indirect nature of its energy band gap, bulk
silicon is indeed a highly inefficient light emitter. There have
been different approaches developed to overcome this problem,
quantum confinement in silicon nanostructures and rare earth doping
of crystalline silicon have received a great deal of attention. Of
particular interest is silicon nanoclusters (NC) embedded in
SiO.sub.2 in recent years attracted interest of the scientific
community as a promising new material for the construction of
visible Si-based Light Emitting Diodes (LED).
[0007] The telecommunications industry commonly uses optical fibers
to transmit large amounts of data in a short time. One common light
source for optical-fiber communications systems is a laser formed
using erbium-doped glass. One such system uses erbium-doped glass
fibers to form a laser that emits at a wavelength of about 1.536
micrometer and is pumped by an infrared source operating at a
wavelength of about 0.98 micrometer. One method usable for forming
waveguides in a substrate is described in U.S. Pat. No. 5,080,503
issued Jan. 14, 1992 to Najafi et al., which is hereby incorporated
by reference. A phosphate glass useful in lasers is described in
U.S. Pat. No. 5,334,559 issued Aug. 2, 1994 to Joseph S. Hayden,
which is also hereby incorporated by reference. An integrated optic
laser is described in U.S. Pat. No. 5,491,708 issued Feb. 13, 1996
to Malone et al., which is also hereby incorporated by
reference.
[0008] There is a need in the art for an integrated optical system,
including one or more high-powered lasers along with routing and
other components that can be inexpensively mass-produced. The
system should be highly reproducible, accurate, and stable.
SUMMARY OF THE INVENTION
[0009] According to one broad aspect, the invention provides an LED
comprising REDGIVN (rare earth doped group IV nanocrystal)
material.
[0010] In some embodiments, the LED comprises in sequence: a
conductive substrate and/or bottom cladding; the REDGIVN in a
REDGIVN film; a conductive and transparent layer on top of the
REDGIVN film; a first contact on top of the conductive and
transparent layer and a second contact on the substrate; wherein
the LED is turned on by applying a voltage across the first contact
and the second contact.
[0011] In some embodiments, the substrate is selected from a group
consisting of: comprises p or n silicon substrate or Transparent
metal oxide semiconductors such as Zinc Oxide and III V compound
semiconductor substrates, and diamond substrate; the REDGIVN layer
is a silicon rich silicon oxide (SRSO) film containing silicon
nanocrystals doped with a rare-earth precursor; the conductive and
transparent layer comprises a poly-silicon layer.
[0012] In some embodiments, the LED further comprises a small
aperture etched through the first contact to allow emitted light
out.
[0013] In some embodiments, the first contact is a serpent contact
to allow emitted light out.
[0014] In some embodiments, the LED comprises additional rare earth
dopants in the REDGIVN layer so as to produce multiple colours.
[0015] In some embodiments, the LED comprises rare earth dopants
for red, green and blue so as to produce white light.
[0016] In some embodiments, the LED comprises a plurality of layers
of REDGIVN each separated by a buffer layer, and each containing a
respective rare earth dopant.
[0017] In some embodiments, said plurality of layers of REDGIVN
comprise three layers, one each for red, blue and green light.
[0018] In some embodiments, the rare earth ion are selected from a
group consisting of: for blue light: Tetrakis(2,2,6,6
tetramethyl-3,5-heptanedi- onato)cerium(IV) and Ce(TMHD).sub.4; for
a green light: Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)erbium
(III) Er.sup.+3(THMD).sub.3; for a red light:
Tris(2,2,6,6-tetramethyl-3,5-hept- anedionato)europium (III) and
Eu(TMHD).sub.3.
[0019] In some embodiments, the conductive substrate and/or bottom
cladding are also transparent so as to allow some light to exit out
the bottom of the device.
[0020] In some embodiments, there is provided an array of LEDs.
[0021] In some embodiments, different rare earth dopants are used
in respective subsets of the array.
[0022] In some embodiments, an array of LEDs is arranged in groups
of three, each group of three including a red light LED, a green
light LED and a blue light LED so as to produce an overall white
light LED.
[0023] In some embodiments, each LED is individually
actuatable.
[0024] In some embodiments, each of the three LEDS has a respective
different rare earth dopant so as to produce one of red, green and
blue light.
[0025] In some embodiments, each of the three LEDs is individually
actuatable.
[0026] In some embodiments, the group of LEDs is collectively
actuatable.
[0027] According to one broad aspect, the invention provides an
optical laser comprising REDGIVN material.
[0028] In some embodiments, An optical laser comprises: at least
one waveguide comprising a REDGIVN channel; at least one feedback
element(s) defining a laser- laser-resonator cavity in the
waveguide so that laser light is output from the waveguide when
pumped; a pump source.
[0029] In some embodiments, the pump source is a broadband optical
pump source.
[0030] In some embodiments, the pump source is an electrical pump
source.
[0031] In some embodiments, an optical laser comprises a substrate
and/or bottom cladding below the waveguide and a top cladding.
[0032] In some embodiments, the laser cavity has a size, which is
tuned to an excitation wavelength of the rare earth dopant.
[0033] In some embodiments, the at least one feedback element(s)
comprise a first highly reflective mirror, and a second output
coupler mirror which is partially reflective.
[0034] In some embodiments, the at least one feedback element(s)
comprise a first Bragg grating which is highly reflective, and a
second Bragg grating which is which is partially reflective.
[0035] In some embodiments, the feedback elements are frequency
selective, and are tuned to be most reflective near a resonant
frequency of the cavity.
[0036] In some embodiments, an optical laser further comprises
means for varying the wavelength(s) reflected by the feedback
element(s) and varying the effective length of the resonator cavity
to thereby tune the laser to a selected wavelength.
[0037] In some embodiments, an array of lasers is formed on a
common substrate.
[0038] In some embodiments, each laser of the array of lasers has
resonant characteristics and dopants selected to produce a
respective different wavelength.
[0039] In some embodiments, each laser has a respective laser
cavity having a different length.
[0040] In some embodiments, a laser further comprises a Diffraction
Bragg reflector (DBR) grating formed into or close to the waveguide
is used to tune the wavelength of light supported in the waveguide
cavity.
[0041] In some embodiments the resonance characteristics of the
waveguide cavities are individually selected by varying the pitch
of the reflection gratings used to define the cavities which, along
with the effective refractive index for the propagated optical
mode, determines the wavelengths of light reflected by the
gratings.
[0042] In some embodiments, a laser comprises a surface-relief
grating forming a distributed Bragg reflection grating fabricated
on a surface of the wave guide.
[0043] In some embodiments, a laser comprises: a conductive
substrate having a first electrical contact; a transparent
conductive cladding buffer; a layer comprising the wave guide, a
second electrical contact on top of the REDGIVN channel; an
electrical pump source.
[0044] In some embodiments, the at least one feedback element(s)
comprise a high reflecting mirror and output coupler at opposite
ends of the waveguide to form the resonating cavity.
[0045] According to one broad aspect, the invention provides a
laser component comprising: a thin film containing REDGIVN and
having a plurality of waveguides defined by channels within the
substrate; one or more feedback elements for providing optical
feedback to the waveguides to form a respective laser-resonator
cavity in each wave guide with a distinct resonance characteristic
to provide lasing action at a selected wavelength when pumped,
wherein injection of pump light at one or more suitable wavelengths
into the laser-resonator cavity causes output of laser light at the
selected wavelength in accordance with a longitudinal cavity mode
of the cavity.
[0046] In some embodiments, a laser further comprises: a ferrule
having a plurality of spaced-apart attachment sites; and a
plurality of optic fibers attached to the ferrule at a respective
one of the plurality of spaced-apart attachment sites, each optical
fiber also being connected to receive light from a respective one
of the resonator cavities.
[0047] In some embodiments, the laser-resonator cavities have a
plurality of widths on a substrate surface to thereby define a
plurality of effective indices of refraction for the cavities, the
wavelength of a longitudinal cavity mode being dependent
thereon.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] Preferred embodiments of the invention will now be described
with reference to the attached drawings in which:
[0049] FIG. 1 is a schematic diagram of a first LED which uses
Group IV semiconductor nanocrystals doped with rare-earth ions,
provided by an embodiment of the invention;
[0050] FIG. 2 is a schematic diagram of another LED provided by an
embodiment of the invention, adapted to produce white light;
[0051] FIG. 3 is a schematic of an array of LEDs provided by an
embodiment of the invention;
[0052] FIG. 4 is a schematic diagram of a Fabry-Perot Cavity laser
provided by an embodiment of the invention;
[0053] FIG. 5 is a schematic diagram of a distributed feedback
laser provided by an embodiment of the invention;
[0054] FIG. 6 is a schematic diagram of an array of DFB lasers
provided by an embodiment of the invention;
[0055] FIG. 7 is a schematic diagram of an array of v-grooved
lasers; and
[0056] FIG. 8 is a schematic diagram of an electrically pumped SRSO
laser provide by another embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0057] Applicants provisional application <attorney docket
50422-1> entitled "Preparation of type IV Semiconductor
Nanocrystals Doped with Rare-earth Ions and Product Thereof" filed
Jan. 22, 2003 teaches methods of preparing group IV semiconductor
nanocrystals doped with rare-earth ions. In one embodiment provided
in that application, the invention provides a doped type IV
semiconductor nanocrystal layer. In another aspect, the invention
provides a doped type IV semiconductor nanocrystal powder
comprising crystals of a group IV element that bear on their
surface atoms of one or more rare earth elements. The powder can
also be used to form a layer, for example by including the powder
in a layer of a dielectric medium for example spin on glass, or a
polymer. That application is incorporated herein in its entirety by
reference. Two regular applications <attorney dockets 50422-7;
50422-8> have been filed the same day as this application and
are hereby incorporated by reference in their entirety. In the
entire description that follows, whenever a rare-earth doped group
IV nanocrystal material (REDGIVN material) is referred to, any
material taught in the incorporated documents is contemplated.
[0058] FIG. 1 shows an example structure of an LED that is formed
by a Metal Oxide Semiconductor (MOS) structure provided by an
embodiment of the invention. This structure uses a p silicon
substrate 100 which might for example have a resistivity of 0.001.
Any other suitable bottom layer could alternatively be used, for
example Zinc Oxide, or Diamond. Preferably the substrate is
conductive. On top of the substrate 100 there is a REDGIVN layer
102, for example in the form of an Er:SRSO film. On top of the
REDGIVN layer 102 is a conductive, transparent layer 108. This
might for example be polysilicon, but other materials may
alternatively be used. A bottom first contact 106 is shown below
the substrate 100, and a second top contact 104 is shown on top of
the conductive transparent layer 108. Also shown is an opening 107
in the top contact layer 104 to allow light to escape.
[0059] In operation, the REDGIVN layer 102 is activated by applying
a voltage across the two contacts 104,106. The substrate 10 and the
transparent conductive layer 108 serve to spread the field created
between the two contacts such that substantially all of the REDGIVN
layer 102 is activated. The electric field excites the nanocrystals
in the REDGIVN layer 102 which in turn excite the rare earth
dopants, which then emit at the characteristic wavelengths of the
rare earth element.
[0060] There are several ways of making the device of FIG. 6. The
incorporated applications in particular teach a number of ways of
forming the REDGIVN layer 102. In an example process of making the
device of FIG. 6 that assumes that silicon nanocrystals are
employed in the REDGIVN layer 102, the p silicon substrate 100 is
cleaned and etched to remove any oxide on the silicon substrate.
This cleaned and etched substrate is placed into an ECR PECVD
reactor and then exposed to argon plasma for 3 min after pump down
to do a final clean off the silicon substrate. During the plasma
clean the substrate is brought up to 300.degree. C. silicon
substrate, which might for example be n-- type with a conductivity
of 0.05-0.001 .OMEGA.cm, is kept at this temperature during the
Silicon Rich Silicon Oxides (SRSO) film growth. A rare-earth
precursor is also turned on during the SRSO growth to dope the
silicon nanocrystals. The doped SRSO film is grown, preferably from
10 nm to 1000 nm and more preferably from 100 nm-250 nm in
thickness. The refractive index of this film can be measured with a
ellispometer during the deposition and the silane flow adjusted to
have the index of refraction be 1.85 to 1.9. This allows the SRSO
film to have a Si content on the order of 42-45 at %. This is to
insure high conductivity of the SRSO film and small Si nanocrystals
on the order of 1 nm diameter. Other values can be employed. The
rare earth precursor and oxygen are turned off and a doped p.sup.+
poly-silicon layer 108 of 10 nm-50 nm thickness and a conductivity
of 0.001 for example is grown on top of the SRSO film. An element
may be introduced into semiconductor to establish either p-- type
(acceptors) or n-- type (donors) conductivity; common dopants in
silicon: p-- type, boron, B; n-- type phosphorous, P, arsenic, As,
antimony, Sb. This is to make sure of a good transparent current
sheet for a top electrode. The grown structure is then placed in a
RTA furnace and annealed at 950.degree. C. for 5 minutes to form
the nanocrystals and optically activate the rare earth ions into
it's 3+ or 2+ valance states. The result is an erbium doped SRSO
film 102. After the anneal step a top contact Aluminum film 104 for
example of 250 nm-1000 nm thick is deposited on top of the doped
p.sup.+ poly-silicon-Er:SRSO film 102. More generally any of the
conductive metals can be employed. Aluminum has a good work
function energy level so that an ohmic conductor can be made with
the boron doped p.sup.+ poly-silicon layer. Gold would work but may
need to have a chrome layer applied first or else it will peel and
flake off the surface. The bottom contact 106 is also deposited on
to the silicon substrate of a thickness of 500 nm-2500 nm
thickness. An anneal of 450.degree. C. for 5 minutes is performed
to form a ohmic contact on the back side of the n.sup.+ silicon
substrate. In one embodiment, the small aperture 107 is etched
through the top Aluminum contact 104 to allow emitted light 109
out. In another embodiment, a serpent top front contact can be
employed to allow light exit.
[0061] An appropriate selection of the rare earth ion can be used
to tailor the colour of the emitted light 109 from the prepared
LED. For a blue light emitting diode, the rare earth metal
precursor can be selected from
Tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)cerium(IV) and
Ce(TMHD).sub.4. For a green light emitting diode, the rare earth
metal precursor can be selected to be
Tris(2,2,6,6-tetramethyl-3,5-heptanediona- to)erbium (III)
Er.sup.+3(THMD).sub.3. For a red light emitting diode, the rare
earth metal precursor can be selected from
Tris(2,2,6,6-tetramethyl-- 3,5-heptanedionato)europium (III) and
Eu(TMHD).sub.3. This selection of rare earth metal ion precursors
is not meant to be limiting.
[0062] In another embodiment, in order to extract light also from
the bottom of the LED, the layer below the REDGIVN layer 102 is
also transparent (but still conductive), and an appropriately
shaped bottom contact is employed.
[0063] FIG. 1 is an example of a white light LED structure based on
the structure of FIG. 1 but with the REDGIVN layer 102 replaced
with a REDGIVN layer 110 doped with three different rare earth
ions, one for each of blue, red and green light to generate three
different types of light which collectively produce a white light
emission 111. The layer 110 can be formed by simultaneously doping
using different rare earth ions. In a preferred embodiment, a
separate layer is used for each dopant. In some embodiments a
buffer layer, for example of p.sup.+ poly silicon, is provided
between each rare earth layer. In one example, the active region
consists of a layer of REDGIVN doped with a first rare earth ion, a
buffer layer of p.sup.+ polysilicon, a second layer of REDGIVN
doped with a second rare earth ion, a buffer layer of p
polysilicon, and a third layer of REDGIVN doped with a third rare
earth ion, with the three layers containing respective dopants to
produce red, green and blue. More generally any combination of
dopants may be employed.
[0064] Referring now to FIG. 3, shown is an array of LEDs provided
by an embodiment of the invention. In the illustrated example,
there are twelve LEDs 112, . . . ,123 each based on the above
described embodiment. LEDs 112,115,118,121 are blue LEDs; LEDs
113,116,119,122 are green LEDs, and LEDs 114,117,120,123 are red
LEDs, the colour of each LED being determined by the appropriate
selection of the rare earth dopant. The LEDs are also shown in four
groups 124,125,126,127 of three LEDs, each group containing a
respective LED of each of the three primary colours. Each such set
of three LEDs can be used to form a white light LED. In one
embodiment, each of the colours making up the group of three is
individually actuatable so as to produce a desired colour. In
another embodiment, all three LEDs in a group turn on together to
produce white light at a point a distance from the device where
substantial combination of light has taken place. The arrangement
of FIG. 3 can be made using a single layered process by applying
the three rare earth dopants in three separate stages while masking
the remaining areas. While specific examples of different colours
are shown in FIG. 3, it is to be understood that an arbitrary array
of LEDs is contemplated.
[0065] Another embodiment of the invention provides a planar
optical laser that is manufactured by using IV semiconductor
nanocrystals that are doped with rare-earth ions such as Scandium,
Yttrium and the Lanthanides. The purpose of this technology is to
allow one to develop an inexpensive method of manufacturing planar
optical lasers for use in the telecommunication industry but is not
limited to just that field. This technology is also applicable in
advanced high speed back-planes and other high speed hybrid
optoelectronic circuits.
[0066] Preferably the planar optical laser is fabricated on a flat
substrate such as fuse silica and or silicon and other such
suitable substrate material. The substrate could also be of a
flexible nature assuming that the nanocrystal layer did not crack
or peel due to the flexible nature of the substrate. By using
silicon wafers as the substrate one then gains access to
well-established process and fabricating manufacturing facilities
throughout the world. Also by developing the flexible substrate
technology one would be able to exploit roll-web processes, which
would allow one to print the Planar Optical Circuits, as one would
do for newspaper, magazines and other such printing
technologies.
[0067] One embodiment provides optical structures and methods for
producing tunable waveguide lasers. In one embodiment, a waveguide
is defined within a glass substrate doped with a rare-earth element
or elements by PECVD. Feedback elements such as mirrors or
reflection gratings in the waveguide further define a
laser-resonator cavity so that laser light is output from the
waveguide when pumped optically or otherwise. The wavelengths
reflected by the reflection gratings can be varied and the
effective length of the resonator cavity can be varied to thereby
tune the laser to a selected wavelength. For example, having a
Bragg reflector as one of the feedback mirrors would allow the
cavity to have a preferential high Q for the resonate of the Bragg
reflector which then would re-enforce the laser frequency. The
Bragg grating could be made to have a varying frequency response by
having the grating tuned, for example by thermal or mechanical
stressor a combination of these.
[0068] Another embodiment provides apparatus and methods for
integrating rare-earth doped lasers and optics on glass substrates.
The invention includes a laser component formed from a glass
substrate with REDGIVN regions defining a plurality of waveguides
defined by channels within the substrate. The laser component may
constitute a monolithic array of individual waveguides in which the
waveguides of the array form laser resonator cavities with
differing resonance characteristics. The channels defining the
waveguides may for example be created by exposing a surface of the
substrate to which a photo resist is spin on and a mask having a
plurality of line apertures corresponding to the channels, which
are to be formed. Other processes may be employed.
[0069] Another embodiment provides a laser component that includes
a thin film doped with one or more optically active rare earth
(preferably lanthanide) species and type IV nanocrystals and having
a plurality of waveguides defined by channels within the film. As
used herein, a "channel within the film" is meant to broadly
include any channel formed on or in the substrate, whether or not
covered by another structure or layer of substrate. Each substrate
waveguide (or "channel") is defined within the substrate as a
region of increased index of refraction relative to the substrate.
The semiconductor nanocrystal glass film is doped with one or more
optically active rare earth species which can be optically pumped
(typically a rare-earth element such as Er, Yb, Nd, or Pr and or
other lanthanide elements or a combination of such elements such as
Er and Yb) to form a laser medium which is capable of lasing at a
plurality of frequencies. Again, any of the layered structures of
the incorporated embodiments may be used to form a suitable laser
medium. Mirrors or distributed Bragg reflection gratings may be
located along the length of a waveguide for providing feedback to
create a laser-resonator cavity. One or more of the mirrors or
reflection gratings is preferably made partially reflective for
providing laser output.
[0070] An example of a waveguide laser based Fabry-Perot Cavity
laser is shown in FIG. 4. This example shows a substrate 130 which
may for example be silica, but could be any other appropriate
substrate material. On top of this is a cladding layer 132, a core
wave guiding layer 134, and a top cladding layer 136. The wave
guiding layer 134 also contains REDGIVN. Also shown is an HR (high
reflectivity) mirror 138 and an OC (output coupler) mirror 140. The
arrangement of FIG. 4, when pumped, spontaneously emits a light
which resonates and eventually exits as output light source 142
through the OC mirror 140 which is partially reflective to allow
some light to escape. The laser of FIG. 4 is preferably optically
pumped.
[0071] In the arrangement of FIG. 4, the feedback components
employed are in the form of the pair of mirrors 138,140. This
produces a Fabry-Perot Cavity. The laser component may constitute a
monolithic array of individual waveguides in which the waveguides
of the array form laser resonator cavities with differing resonance
characteristics (e.g., resonating at differing wavelengths). The
component may thus be used as part of a laser system outputting
laser light at a plurality of selected wavelengths.
[0072] The frequency response of the arrangement of FIG. 9 is
generally indicated at 143 where it has been assumed that Erbium
was used as the rare earth dopant. The size of the cavity (distance
between HR mirror 138 and OC mirror 140) is tuned to resonate near
the active frequencies for Er. This results in the lasing to occur
at the active frequencies for Er which include a dominant frequency
and several other nearby frequencies which are emitted with less
power as shown. In general, the cavity size is preferably
substantially matched to the peak in the fluorescence response for
the particular rare earth dopant to achieve peak efficiency.
[0073] In certain embodiments of the invention, the resonance
characteristics of a waveguide cavity are varied by adjusting the
width of the channel formed in the film, which thereby changes the
effective refractive index of the waveguide. The effective
refractive index can also be changed by modifying the diffusion
conditions under which the waveguides are formed as described
below. A diffraction Bragg reflector (DBR) grating formed into or
close to the waveguide is used, in some embodiments, to tune the
wavelength of light supported in the waveguide cavity. Changing the
effective refractive index thus changes the effective wavelength of
light in the waveguide cavity, which determines the wavelengths of
the longitudinal modes supported by the cavity. In another
embodiment, the resonance characteristics of the waveguide cavities
are individually selected by varying the pitch of the DBR
reflection gratings used to define the cavities that, along with
the effective refractive index for the propagated optical mode,
determines the wavelengths of light reflected by the gratings. In
still other embodiments, the location of the gratings on the
waveguide is varied in order to select a laser-resonator cavity
length that supports the desired wavelength of light.
[0074] In one embodiment, a surface-relief grating forming a
distributed Bragg reflection grating is fabricated on the surface
of the waveguide, for example by coating the surface with photo
resist, defining the grating pattern in the photo resist
holographically or through a phase mask, developing the photo
resist pattern, and etching the grating pattern into the waveguide
with a reactive ion system such as an argon ion mill. In certain
embodiments, a more durable etch mask allowing more precise etching
and higher bias voltages is obtained by depositing chromium on the
developed photo resist pattern using an evaporation method which
causes the chromium to deposit on the tops of the grating lines.
This forms a much more durable mask for the reactive ion system
allowing a deeper etch which would be required for a thicker active
volume.
[0075] An example of a distributed feedback laser based on the
above embodiment is shown in FIG. 10. This embodiment shows a
substrate 152, bottom cladding 160, core 162 and top cladding 164.
The reflecting components consist of an HR mirror 150 and an OC
mirror 154. In this embodiment, the core is in the form of a
distributed bragg reflection grating which might for example have
been formed as described above. The shape used to show the core is
illustrative of the Bragg grating characteristic that concerns an
oscillating index of refraction, and is not necessarily indicative
of the physical shape of the core. The core also contains
rare-earth doped nanocrystals. The OC mirror 154 in this example is
slightly less reflective than the HR mirror resulting in light 166
exiting the arrangement and forming the output of the laser. In
this embodiment, the cavity again defines the wavelength of the
laser and this needs to be substantially set near the active
wavelengths of the rare earth dopants. Preferably, the grating 162
is also tuned to one of these wavelengths. This causes the
arrangement to lase substantially at the single frequency for which
the arrangement is tuned. Thus, the frequency response of this
arrangement, shown generally at 155 has a single peak.
[0076] A first example of an array of lasers will now be described
with reference to FIG. 6. In this example, there are four lasers
generally indicated by 210,212,214,216. Each laser 210,212,214,216
has a respective first Bragg grating 170,172,174,176 (although
other reflective elements may alternatively be employed) a
respective core area 178,180,182,184 forming a laser cavity and a
respective second Bragg grating 188,190,192,194 (although other
output reflective elements can be employed. In the illustrated
example, one set of gratings 170,172,174,176 is almost completely
reflective for example having 99% reflectivity. The other set of
gratings 1788,180,182,184 is slightly less reflective to allow some
light through as an output signal. In the illustrated example, the
second set has 96% reflectivity.
[0077] The lasers have outputs 200,202,204,206 which generate
wavelengths .lambda.n, .lambda.3, .lambda.2, .lambda.1
respectively. It is of course to be understood that any number of
lasers can be included in an array such as the array of FIG. 6.
Four are shown simply by way of example. Here, the characteristics
of each laser in the array are tuned to generate the respective
wavelength. This can be done by adjusting the first and second
bragg gratings of a given laser and/or by adjusting the length of
the cavity. As in previous embodiments, the core region of each
laser is constructed using SRSO doped with rare-earth ions. The
array of lasers of FIG. 6 can be formed in a single layered
structure with the four lasers being side by side in a respective
channel within the substrate for example. The frequency response of
the arrangement of FIG. 6 is generally indicated at 201, and shows
a respective frequency for each laser. In this case, by tuning the
bragg gratings a narrow frequency response can be generated for
each laser output.
[0078] An individual laser can also be formed using the embodiment
of FIG. 6. Furthermore, in another embodiment, the arrangement of
FIG. 6 is provided, but oriented orthogonally to the arrangement
shown. This consists of a substrate, a first layer containing a
Bragg grating, a second layer containing the core/cavity, and a
third layer containing a second partially reflective Bragg grating.
This arrangement produces a laser that emits light out the top of
the device.
[0079] FIG. 7 is another example of an array of lasers provided by
an embodiment of the invention. Again, the array is shown to
include four separate lasers 350,352,354,356, but any appropriate
number of lasers could alternatively be provided. In this
embodiment, each laser has an HR mirror 300,302,304,306, and an
active SRSO segment 310,312,314,316. The active SRSO segment of
each laser is followed by an output coupler 360,362,364,368. The
arrangement thus far is substantially similar to the arrangement of
FIG. 6, which was a perspective view whereas the view of FIG. 7 is
a top view. The output couplers 360,362,364,368 couple the output
of the active SRSO segments 310,312,314,316 into a v groove section
320,322,324,326 that in turn is coupled to output fibers
330,332,334,336 connected to output couplers 340,342,344,346.
[0080] In a variant of the above described embodiment, the output
fibers can be attached to a single a ferrule having a plurality of
spaced-apart attachment sites.
[0081] The embodiments above have assumed optical pumping. More
generally several examples of methods of pumping REDGIVN are
provided in applicant's co-pending application no. <attorney
docket no. 50422-5> filed on the same day as this application
which is based on U.S. provisional application No. 60/441485
hereby, both of which are hereby incorporated by reference in their
entirety. Those applications involve pumping for the purpose of
amplification. However, the same principles are applicable here for
pumping in the context of lasers. Optical pumping and electrical
pumping are disclosed and contemplated for these laser
applications.
[0082] When electrical pumping is used instead of optical pumping
the substrate is conductive, for example an n.sup.+ silicon
substrate, to which a transparent conductive cladding buffer such
as zinc oxide (ZnO) film, for example of from 2000 to 6000 nm, is
applied. A REDGIVN film, for example having a thickness of from 100
to 500 nm, is deposited on transparent conductive layer and
annealed. A top electrical contact, for example 500-1000 nm of
Indium Tin Oxide (ITO), is deposited on top of the REDGIVN film.
Alternatively, a p.sup.+ poly-silicon layer can also be used as
well as a cadmium oxide CdO film and other metal oxides. One would
make the choice based on whether the REDGIVN film is a positive
(hole) donor or negative (electron) donor. This is then masked and
etched to form a active waveguide in which HR mirror and output
coupler placed at each end of the waveguide to form the resonating
cavity.
[0083] FIG. 8 shows an example featuring electrical pumping. Shown
is an n+ silicon substrate 400 having a bottom electrical contact
402. Shown is a ZnO film 406 on top of the n+ silicon substrate
400. On top of the ZnO film there is a layer of rare-earth doped
SRSO film 408 to which is applied a top contact layer 404 which
might for example be Indium Tin Oxide as in the above example. As
in some previous embodiments, shown is an HR mirror 410 and an
output coupler 412 through which an output light signal 414 passes.
More generally, the electrical pumping can be used for any of the
embodiments described herein with appropriate modifications.
[0084] Numerous modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practised otherwise than as
specifically described herein.
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